[and now, after that]: After the Savior has “showed himself unto his people” (verse 2). Moroni takes this as a reference to the visitation of the Savior to the New World, not the Old World. This personalization of the commandment and the timing allows Moroni to reflect on what has become of his people since the Savior had appeared to them, and what has happened is that they “have all dwindled in unbelief.”
[therefore I am commanded that I should hide them up again in the earth]: The beginning point of this statement is that information from the brother of Jared was hidden up for the right time. Now, the unbelief of the people around Moroni requires that he too hide up sacred things until the right time. Moroni is seeing a parallel between his record and that of the brother of Jared. This parallel is certainly assisted by the information on the unreadability of the record without the interpreters, which interpreters Moroni by now understands that he will be hiding up for that same future purpose in connection with his father’s work.